Field T rip Guide Book - P09

Transcription

Volume n° 3 - from D01 to P13
Field Trip Guide Book - P09
32nd INTERNATIONAL
GEOLOGICAL CONGRESS
Florence - Italy
August 20-28, 2004
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IGNIMBRITIC DEPOSITS IN
CENTRAL ITALY:
PYROCLASTIC PRODUCTS
OF THE QUATERNARY AGE
AND ETRUSCAN FOOTPATHS
Leader: G. Nappi
Associate Leaders: L. Valentini, M. Mattioli
Post-Congress
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The scientific content of this guide is under the total responsibility of the Authors
Published by:
APAT – Italian Agency for the Environmental Protection and Technical Services - Via Vitaliano
Brancati, 48 - 00144 Roma - Italy
Series Editors:
Luca Guerrieri, Irene Rischia and Leonello Serva (APAT, Roma)
English Desk-copy Editors:
Paul Mazza (Università di Firenze), Jessica Ann Thonn (Università di Firenze), Nathalie Marléne
Adams (Università di Firenze), Miriam Friedman (Università di Firenze), Kate Eadie (Freelance
indipendent professional)
Field Trip Committee:
Leonello Serva (APAT, Roma), Alessandro Michetti (Università dell’Insubria, Como), Giulio Pavia
(Università di Torino), Raffaele Pignone (Servizio Geologico Regione Emilia-Romagna, Bologna) and
Riccardo Polino (CNR, Torino)
Acknowledgments:
The 32nd IGC Organizing Committee is grateful to Roberto Pompili and Elisa Brustia (APAT, Roma)
for their collaboration in editing.
Graphic project:
Full snc - Firenze
Layout and press:
Lito Terrazzi srl - Firenze
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Volume n° 3 - from D01 to P13
32nd INTERNATIONAL
GEOLOGICAL CONGRESS
IGNIMBRITIC DEPOSITS
IN CENTRAL ITALY:
PYROCLASTIC PRODUCTS
OF THE QUATERNARY
AGE AND ETRUSCAN
FOOTPATHS
AUTHORS:
G. Nappi, L. Valentini, M. Mattioli (Università di Urbino - Italy)
Florence - Italy
August 20-28, 2004
Post-Congress
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Front Cover:
Necropolis of Sovana, Tomba Ildebranda.
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P09
IGNIMBRITIC DEPOSITS IN CENTRAL ITALY: PYROCLASTIC PRODUCTS
OF THE QUATERNARY AGE AND ETRUSCAN FOOTPATHS
1 - Introduction
This three-days field trip will cover three important
volcanic districts in central Italy: the Vulsini and
Vico Volcanic Districts, which belong to the Roman
Comagmatic Province, and the Cimini Volcanic
District (Figure 1). The field trip will provide
participants with an opportunity to examine some
of the most studied pyroclastic flow deposits in
the world in their most significant exposures. The
pyroclastic flow deposits in this area are characterized
by a broad spectrum of peculiar features in terms
of composition, component distribution, grain-size,
degree of welding, structures, depositional sequences,
geometries, and their relationships to eruptive and
depositional mechanisms. The planned itinerary will
enable participants to observe first hand the structural
and textural characteristics of these products, and
of their main depositional facies within the relative
stratigraphic sequences. One of the main goals of the
field trip is to stimulate discussion on the possible
mechanisms developed during the respective transport
and depositional phases.
Some stops will also allow us to gain insight into the
relationships between the geology of the area and the
history of its towns. Many of these pyroclastic flow
deposits have been intensively quarried and shaped by
man. Several examples will be visited, starting from
Etruscan graves, through Roman monuments up to
modern buildings.
2 - Geological setting
The Quaternary ignimbrite-forming eruptions are
related to the post-collisional volcanism of the eastern
Tyrrhenian border. This potassic-alkaline volcanism
developed during the Quaternary period along the
Tyrrhenian margin of Italy, from the northern Vulsini
District to the southern Vesuvio-Phlegrean Fields’
volcanic structures. The area of southern Tuscany and
Latium has been affected since the Plio-Pleistocene
period by intense magmatic activity, with a migration
in time and space of the feeding fissures from west
to east, and important changes in the nature of the
erupted magma. The Pliocene magmatic activity
began along the Tyrrhenian border, with emplacement
of intrusive bodies and extrusions of crustal anatectic
magmas. During the Pleistocene period some volcanic
Volume n° 3 - from DO1 to P13
Leader: G. Nappi
Associate Leaders: L. Valentini, M. Mattioli
Figure 1 - Geological sketch of the northern Roman Comagmatic Province in Central Italy (modified after Locardi
and Molin, 1974). Symbols: 1 = Alkaline potassic volcanics (Pleistocene to Recent): a) Vulsini volcanoes,
b) the Vico volcano, c) Sabatini volcanoes, d) Alban Hills volcanoes; 2 = acidic volcanics (Plio-Pleistocene);
3 = travertine; 4 = Recent (continental and coastal sediments); 5 = Upper Miocene-Lower Pleistocene (clay and sand);
6 = Carboniferous-Lower Miocene (sedimentary sequences); 7 = faults; 8 = buried faults.
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Figure 2 - Structural map of the Vulsini Volcanic District (modified after Nappi et al., 1991).
Symbols: 1 = deep faults; 2 = faults; 3 = caldera rims; 4 = buried caldera rims; 5 = cinder cones;
6 = buried cinder cones; 7 = central explosive eruption; 8 = maars; 9 = dome-like structures;
10 = explosion craters; 11 = surtseyan activity; 12 = eruptive centres; 13 = buried eruptive centres;
14 = sulphurous activity; 15 = thermal springs; 16 = mineral springs.
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acid products of Tuscan affinity, as well as products
with Lamproitic affinity, were erupted (1.3 – 0.9 Ma).
The Cimini Volcanic District was formed during 1.35
– 0.95 Ma (Evernden and Curtis, 1965; Nicoletti,
1969), whereas the products of the three main volcanic
districts, Vulsini, Vico and Sabatini, were erupted
between 0.6 and 0.1 Ma (Figure 1). The volcanic
rocks of these districts display a broad compositional
spectrum with magmas belonging to the two distinct
evolutionary series, called the potassic (KS) and highpotassic (HKS) series (Appleton, 1962; Peccerillo and
Manetti, 1985).
According to Beccaluva et al. (1991), the volcanism
in the Roman Comagmatic Province can be related
to the partial melting of heterogeneously-enriched
mantle sources. Serri et al. (1993) suggest that mantle
sources of the northern Apennine arc’s magmatism can
be explained by a geodynamic process which causes
a large amount of crustal material to be incorporated
within the upper mantle. More recently, Peccerillo
(2002) suggests that the variety of magmas in centralsouthern Italy reflects a mosaic of compositionallydistinct, pre-metasomatic mantle sources that were
modified by different metasomatic events.
2.1 The Vulsini Volcanic District
The Vulsini Volcanic District (hereafter VVD) was
developed around 600-100 ka, between Tuscany and
Latium, covering an area of about 2000 km2 (Figure
1). The Bolsena and Latera calderas represent the
two main polygenetic structures which developed
during the activity of the whole VVD (Figure 2).
The volcano-tectonic caldera of Bolsena (16 km in
Figure 3 - Chronostratigraphic sketch of the Vulsini
Volcanic Zones. PVZ = the Paleobolsena Volcanic Zone;
BVZ = the Bolsena Volcanic Zone; LVZ = the Latera
Volcanic Zone; MVZ = the Montefiascone Volcanic Zone;
NVZ = the Neobolsena Volcanic Zone;
CAF = the Civitella d’Agliano Formation; OBI = OrvietoBagnoregio Ignimbrite; OF = the Onano Formation;
PF = the Pitigliano Formation. Symbols: 1 = pumice fall;
2 = pyroclastic flow; 3 = lava flow; 4 = ash fall;
5 = surtseyan deposits; 6 = sedimentary substratum.
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Figure 4 - Space-time evolution of the Vulsini Volcanic Zones visualized through a schematic cross section from W to
E of the District (modified from Nappi et al., 1995). Symbols: 1 = clayey-sandy and conglomeratic sediments of marine
and brackish environments; 2 = mainly back-fall lithic breccias; 3 = conjectural effusive activity older than the dated
plinian pumice falls; 4 = Basal plinian pumice falls; 5 = pyroclastics and lavas; 6 = the Civitella d’Agliano Formation;
7 = mainly back-fall lithic breccias; 8 = pyroclastics and lavas; 9 = Vietena lavic plateau; 10 = Ponticello pumice fall;
11 = Orvieto-Bagnoregio Ignimbrite; 12 = Monterado lava flows; 13 = Montefiascone pyroclastics; 14 = Bisentina
Island surtseyan activity; 15 = pre-caldera effusive phase; 16 = Vulci and Monte Calvo lava flows; 17 = ignimbrites;
18 = the Pitigliano Formation; 19 = post-caldera effusive phase; 20 = post-caldera phreatomagmatic eruptions.
average diameter) is the result of incremental growth
due to subsidence, with the caldera floor hinged on
the SW side, as well as to some volcanic collapses
(Nappi et al., 1991). The Latera caldera, located in the
western sector (Nappi, 1969 a, b; Nappi et al., 1995),
was formed by partially-coalescent collapses which
occurred after several moderate-sized ignimbriteforming eruptions (Figure 2). In the evolution of
the VVD the Paleobolsena, Bolsena, Montefiascone,
Latera and Neobolsena Zones have been distinguished
(Figs. 3 and 4). These zones developed with alternating
effusive, strombolian, plinian and ignimbrite-forming
eruptions. Their products are characterized by a wide
range of compositions belonging to the leucitite,
basanite and shoshonite magmatic suites.
Near-primary magmas and differentiated products
are present within each series. The vast majority
of differentiated products occurs in the Bolsena
and Latera Volcanic Zones, where pyroclastics
were erupted during plinian-type and ignimbriteforming eruptions. On the other hand, abundant,
rather undifferentiated magmas are present in the
Montefiascone Zone. Such magma distribution has to
be related to the structural setting of the sedimentary
substratum. In the Latera, Paleobolsena and Bolsena
Zones, where a front of over-thrust sheet of the
Tuscan sequence is present, relatively large magma
bodies only a few kilometres deep can be inferred.
The shallow magma chamber position at the top of the
fractured carbonate basement in the Montefiascone
Volcanic Zone would have facilitated the uprising of
less evolved magma (Figure 4).
2.1.1 The Paleobolsena Volcanic Zone
The oldest products of the VVD directly overlie
Plio-Pleistocene neoautochthonous sediments and are
represented by three plinian pumice-fall layers (576
± 6.5 ka) and a widespread ignimbrite (Nenfro auct.,
Nappi, 1969a, b; the Civitella D’Agliano Formation,
Aurisicchio et al., 1992; 505 ± 5.7 ka), which
represents the result of the largest ignimbrite-forming
eruption in the VVD (Figure 5). The inferred average
thickness and the areal distribution of this area of
about 1500 km2 suggest a minimum estimated volume
of 10 km3 for this ignimbrite. It can be observed only
in the most peripheral area of the VVD, where it
either overlies a centimetric-thick pumice-fall layer,
or directly lies upon the Plio-Pleistocene sediments.
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Figure 5 - Geological sketch map of the Vulsini Volcanic District (modified after Vezzoli et al., 1987).
Symbols: 1 = Quaternary sedimentary deposits; 2 = travertine; 3 = products of the Torre Alfina center and Vico
Volcanic District; 4 = lava flows; 5 = pyroclastic successions; 6 = effusive and strombolian activity products;
7 = the Pitigliano eruption unit; 8 = the Poggio Pinzo succession; 9 = F, E, e and D Ignimbrites; 10 = C Ignimbrite;
11 = B and A Ignimbrites; 12 = lava flows; 13 = Orvieto-Bagnoregio Ignimbrite; 14 = pyroclastic succession; 15 = lava
flows; 16 = pyroclastic succession; 17 = lava flows; 18 = Nenfro Ignimbrite; 19 = pyroclastic and volcano-sedimentary
successions; 20 = Mesozoic to Quaternary sedimentary substratum; 21 = scoria cones; 22 = craters; 23 = caldera rims;
24 = faults and fractures; A = Acquapendente, B = Bolsena, Ba = Bagnoregio, C = Canino, CA = Civitella d’Agliano,
F = Farnese, G = Grotte di Castro, L = Latera, M = Montefiascone, O = Orvieto, P = Pitigliano, PS = Piano della
Selva, R = La Rocca, S = Sovana, Se = Sermugnano, So = Sorano, T = Tuscania, TA = Torre Alfina.
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Figure 6 - Areal distribution of the main OBI deposits with
the isopleths of the average diameter (in cm) of the five
largest lithic clasts in the uppermost unit (modified from
Nappi et al., 1994b). Symbols: 1 = areal distribution;
2 = Bolsena caldera rim; 3 = isopleths (equidistance 2 cm).
The deposits of the Nenfro eruption are characterized,
from bottom up, by the following facies: a) plinian
basal fallout made up of a widespread pumice
level only a few centimetres thick; b) a pyroclastic
flow deposit consisting of a basal pale-grey level
of reversely-graded fine ashes with a maximum
thickness of 6 cm, followed by a dark-grey welded
deposit (maximum thickness of 6 m) with fine-grained
micropomiceous matrix and vitrophiric “fiamme”. An
unwelded grey deposit, characterized by a coarse-
grained matrix containing
light sanidine-bearing pumices
and dark analcimized leucitebearing pumices, is also
present in the upper part of the
Nenfro sequence.
2.1.2 The Bolsena Volcanic
Zone
During the Bolsena caldera
formation,
there
was
widespread volcanic activity
along or within the inner sector
of the caldera (Figs. 3 and 5).
Lava flows and pyroclastic
products,
trachytic
in
composition, were emplaced.
A large volume of weldedscoria fall was diffusely
emplaced in the area around
Bolsena village from about
390 to 360 ka. Immediately
afterwards, this area was
affected by a large explosive
activity that gave rise to the
Ponticello plinian eruption,
followed by the OrvietoBagnoregio
Ignimbrite
eruption. The Ponticello fall
deposit is exposed in the
north-eastern sector of the
Vulsini area; it reaches a
maximum thickness of 2.5 m
about 2 km east of Bolsena
village. The juvenile fraction
of the Ponticello deposit is
made up of prevailing white
trachytic pumice clasts, and
shows a normal grain-size grading; grey and banded
(mixed) pumices occasionally occur toward the top of
the deposit (Nappi et al., 1994a).
The Orvieto-Bagnoregio Ignimbrite (hereafter OBI)
spreads across the north-eastern sector of the VVD
(Nappi et al., 1994b; Figure 6) and its primary areal
distribution, inferred from the observed outcrops, is
about 200 km2, extending from Bardano, in the north,
to Castel Cellesi, in the south. This eruption was the
result of the emptying of the compositionally-zoned
latite to trachyphonolite magma chamber (Table 1),
and represents the largest explosive event of the
Bolsena Zone.
The OBI eruption took place 333 ± 3 ka (Santi,
1990; Gillot et al., 1991; Figure 3), during the final
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trachyte
trachyte
phonolite
trachyte
SiO2
TiO2
Al2O3
Fe2O3
FeO
MnO
MgO
CaO
Na2O
K2O
P2O5
LOI
59.04
0.48
18.92
0.39
2.36
0.14
0.29
2.38
2.93
8.90
0.04
4.12
60.86
0.51
19.27
0.39
2.36
0.14
0.22
2.21
2.70
9.72
0.04
1.59
58.62
0.45
18.50
3.28
0.12
0.46
2.77
3.53
9.71
0.02
2.54
57.89
0.53
20.30
0.43
2.60
0.15
0.25
2.21
2.89
8.11
0.03
4.60
Table 1 - Chemical analyses of major elements (%wt.) and
classification of the OBI juvenile fragments.
paroxysmal explosive activity of the Bolsena zone,
and gave rise to the emplacement of several pyroclastic
deposits. The stratigraphic series of the OBI can be
summarized in (1) a basal plinian pumice-fall deposit
and (2) a main ignimbrite deposit. The latter is made
up of: (a) a ground-surge which always underlies the
ignimbrite throughout its areal distribution, (b) a nearvent lithic-breccia deposit, (c) a series of thin and
highly-dispersed pumice flow units (lowermost unit)
and (d) a thick, topographically-controlled pyroclastic
flow deposit (uppermost unit).
The OBI is the largest ignimbrite-forming eruption of
the eastern Vulsini area and it can be considered the
most useful chronostratigraphic marker for separating
Bolsena volcanics from the deposits of the upper
Montefiascone Zone (Nappi et al., 1994b).
2.1.3 The Latera Volcanic Zone
The history of the Latera Volcanic Zone (Figs. 3 and
5) can be subdivided into three distinct phases.
The first phase produced mostly lava flows. The
second phase produced a large volume of ignimbrites
and subordinate pyroclastic fall and surge deposits;
it was in this phase that the caldera of Latera was
formed. During the third phase, hydromagmatic and
strombolian activity took place on the rim of the
Latera caldera. Sparks (1975) proposed that the Latera
volcano be considered an ignimbrite shield volcano,
with its low profile so similar to those of many basaltic
shield volcanoes. In fact many ignimbritic units have
been identified and studied in the Latera Zone (Nappi,
1969a, b; Sparks, 1975; Varekamp, 1980; Metzeltin
and Vezzoli, 1983; Capaccioni et al., 1994; Nappi et
al., 1994b; Palladino and Valentine, 1995; Palladino
and Simei, 2002). The first complete and careful study
of the Latera ignimbrite sequence was carried out by
Sparks (1975). This author, in a comprehensive study
on the Latera caldera, named the major (0.3 - 2.2 km3
each) and most widespread ignimbrites sequentially
with capital letters (A, B, C, D, E, F, from the oldest
to the youngest, Figure 7). Smaller ignimbrites (a, b,
c, d, e) also occur within the sequence. The A, B, C
and D Ignimbrites were generated by the collapse
of very high eruptive columns outpoured by central
vents and followed by the formation, in the central
zone, of the present caldera. On the contrary, the final
explosive phases (E, F Ignimbrites and the “Pitigliano
Formation”) added source vents in the northern
sector.
The A Ignimbrite is the oldest ignimbrite and is
exposed widely over all sides of the volcano. This
deposit ranges from poorly-coherent to coherent
and is formed by several layers, which are made up
by decimetric, grey, trachytic pumices with sanidine
phenocrysts in a crystal-rich matrix containing
sanidine, biotite and clinopyroxene. The lithic clasts
are represented by both sedimentary and igneous
types. The A Ignimbrite reaches its maximum
thickness of 45 m far away from the vent.
The B Ignimbrite crops out in the western and
north-eastern sector of the Latera caldera (Figure
5). It appears as a light-brown deposit with an ash
matrix, poor in pumice clasts but very rich in rounded
lava bombs and sedimentary lithic fragments,
olocrystalline nodules and rare accretionary lapilli.
The juvenile fraction consists of two types of pumiceclasts varying in colour from white to dark-grey. The
B Ignimbrite normally shows one or two flow units,
and it reaches a maximum thickness of a few meters.
The C Ignimbrite is the most widely distributed of
the Latera ignimbrites in the south-western sector,
overlying epiclastic lacustrine deposits (Figs. 5 and
7). This ignimbrite, which consists of two pyroclastic
flow units, always shows a pyroclastic surge level at
the base. The basal surge is formed by a horizon of
white ashes and accretionary lapilli. The lower unit
consists of decimetric, white pumices, containing
leucite and sanidine phenocrysts. The upper is a
sillar-type deposit with a red ash-matrix and blackish
pumices. The lithic clasts occur both concentrated at
the base and dispersed throughout the deposit.
The D Ignimbrite is a fine-grained ignimbrite with a
large areal distribution. In the southern sector only one
flow unit occurs; on the contrary, in the northern and
Rock
type
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Figure 7 - Areal distribution of the main ignimbrite
deposits related to the Vulsini calderas (modified after
Nappi et al., 1991). a = Basal Ignimbrites; b = Latera
Ignimbrites; c = Basal Montefiascone Ignimbrite;
d = Orvieto-Bagnoregio Ignimbrite.
B = the Bolsena caldera; L = the Latera caldera;
M = the Montefiascone caldera;
V = the Vepe caldera.
western sectors, many flow units are present (Figs. 5
and 7). The colour ranges from pale-yellow (coherent
sillar deposits) to white (incoherent facies). The lower
flow unit shows a repetition of beds, with reverselygraded, coarse pumices. An orange lithified deposit
in sillar facies, containing sanidine and analcimized
leucite crystals, occurs in the upper part.
The E Ignimbrite is a well-lithified sillar deposit,
which can be found on both the northern and southern
sides of the Latera caldera. Many flow units can
be distinguished on the northern side (Figs. 5 and
7). According to Sparks (1975), this is a complex
ignimbrite produced by a mixed magma, as shown
by the presence of both pale tubular pumices (5 cm
of length) and black scoria clasts (15 cm of length). A
distinctive characteristic of this pyroclastic deposit is
the presence of large tree holes at its bottom. Sparks
also indicates the presence of several ignimbrites
which occur at the same stratigraphic level as the E
Ignimbrite.
The tephriphonolitic F Ignimbrite represents the
final phase of the eruption that gave rise to the
“Vulcanite Complessa di Onano” (Nappi, 1969a,
b). The beginning of this activity is represented by
lava fountaining along a NW-SE eruptive fissure,
mostly coinciding with the NE border of the present
caldera. Products of such activity produced a welded
air-fall deposit, exposed on the northern and eastern
sectors of the Latera caldera (Figure 5). The overlying
pyroclastic flow deposit (F Ignimbrite) is a sillar-type
deposit, light-yellow to reddish in the upper part, and
incoherent, grey to black with breadcrust bombs in
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domes. In the more distal
outcrops, polygenetic layers are
interbedded within the welded
sequence, whose variations in
physical properties, textural
characteristics, and other field
evidence suggest an important
fallout component followed by
rheomorphism.
Furthermore,
the occurrence of variations in
the relative proportions of the
different kinds of near-surface
and deep-seated rocks of the
polygenetic breccia layers
supports the hypothesis of a
progressive opening of several
source vents localized around
the NW rim of the Vepe caldera
(Nappi 1969a, b; Figure 5).
Collapsing eruptive columns,
followed by lava fountains,
respectively
produced
the
lowermost welded sequence
(rheomorphic air-fall tuffs)
and the un-welded sequence
(pumice
flow
deposits).
Nevertheless, during the final
stage of the eruption, lavas
outpoured quietly from a caldera
ring fracture. The eruptive
styles were regulated by the
degree of magma fragmentation
and the rapid subsidence of
a “piston-like” block, which
mostly occurred when the
magma chamber had been
nearly completely tapped, and
the residual melt of the deeper
part of the magma reservoir
was squeezed out, forming
low-angle exogenous domes.
Figure 8 - Evolution of the Montefiascone caldera. Symbols: 1 = caldera rim;
In the final stage of the Latera
2 = areal distribution of the Basal Ignimbrite; 3 = lava flow;
Volcanic Zone, strombolian
4 = hydromagmatic deposits and spatter cones.
eruptions took place within
the lower part. The ash matrix contains leucite and
the caldera (“Mt. Becco”, “Mt.
pyroxene crystals, while feldspars are absent.
Spinaio” and “La Dogana” centres) and along the
The depositional sequence of the “Pitigliano caldera rim (“Valentano” scoria cones).
Formation” (Nappi 1969a, b) is composed of: (a)
basal pumice flow deposits (unwelded sequence), (b) 2.1.4 The Montefiascone Volcanic Zone
rheomorphic welded air-fall tuffs (welded sequence), The structural study of the entire VVD has revealed
which locally transition into lava-like deposits, the presence of a main caldera structure (the
and (c) lava flows that form low-angle exogenous Montefiascone caldera; Marini and Nappi, 1986),
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which has a volume of 1 km3 and is located south-east
of Bolsena Lake (Figure 8). Its sub-circular rim has a
diameter of 3 km with a base diameter of 1.5 km; the
average rim height is 200 m over the Bolsena Lake
level. The Montefiascone caldera lies in an area of
convergence of several fault systems, with dominant
N-S and NE-SW directions. Such tectonic lines have
controlled the eastern Vulsini volcanic activity since
the early phases, with continuous reactivations until
the most recent episodes (Nappi and Marini, 1986a).
A third regional tectonic discontinuity, a fracture
oriented NW-SE, divides the Montefiascone caldera
into two parts.
The evolution of the Montefiascone caldera can be
summarized in the following volcano-tectonic phases:
a) emission of the basal Montefiascone Ignimbrite,
followed by the caldera’s collapse, b) hydromagmatic
activity and a new collapse, followed by circum- and
intra-calderic strombolian activity.
2.1.5 The Neobolsena Volcanic Zone
The Neobolsena Volcanic Zone (Figure 3) developed
within the present Bolsena Lake during the final
stage of the evolution of the Bolsena caldera. The
activity is represented by sub-lacustrine eruptions
of surtseyan-type which produced the Martana and
Bisentina Islands. Although most of the products
are represented by phreatomagmatic tuffs, the final
activity of Bisentina Island is entirely effusive, with
the outpouring of leucite-bearing lava, which shows
the youngest radiometric age among all the Vulsini
volcanic products (127 ± 1.8 ka; Santi, 1990; Gillot
et al., 1991).
2.2 The Cimino Volcanic District
The evolutive history of the Cimino Volcanic District
(hereafter CVD; Figure 1) can be subdivided into three
eruptive phases (Lardini and Nappi, 1987). During the
first phase, endogenous and exogenous domes formed
along NW-SE feeding fissures; explosive activity
followed the domes’ growth, and pyroclastic flows
(which gave rise to the Cimina Ignimbrite) were
generated along the same fissures (Figure 9a, b).
The Cimina Ignimbrite spread out essentially along
the eastern side of the feeding fissures, and covered
an area of about 300 km2, with a maximum thickness
of about 200 m. During the second phase, a few
domes developed along NE-SW fissures, followed
by hydromagmatic activity generating pyroclastic
surges. According to their distribution they seem to
have been generated by explosions inside the domes’
feeding fissures on the eastern part of the present
Cimino Mount. The hydromagmatic products are
characterized by a prevalently planar structure with
reverse grading.
Such products crop out only in the eastern part of
the CVD and show a regular distribution. After
hydromagmatic explosions, another large magmatic
explosive eruption generated a second pyroclastic
flow deposit, which covers an area of 20 km2, with an
average thickness of 10 m. The matrix and the coarse
pumices of the younger pyroclastic flow deposit
show a more marked vesiculation than the older one.
Furthermore, the lithic fragments are smaller in the
younger ignimbrite. In the third and final cycle a
central volcano developed.
2.3 The Vico Volcanic District
The Vico Volcano (hereafter VV; Figure 1) can be
considered a central strato-volcano with a caldera
depression at its summit. The VV developed on
complicated regional structures, consisting of a
graben elongated NW-SE and a very important
tectonic fracture directed NE-SW (the Orte-Vico
fault). The VV activity extended between 419 ka and
95 ka, and its volcanic history can be summarised in
four phases: (1) a prevalently explosive plinian-type
activity, (2) a predominantly effusive activity, with
the formation of the strato-volcano, (3) ignimbriteforming eruptions and caldera genesis, and (4)
circum-caldera hydromagmatic and strombolian
eruptions.
The products of the first phase consist of several
plinian fall deposits with wide areal distribution,
which are spread out northward and eastward from
the inferred central crater. The second phase is
characterized by the building of the cone by lava
flows, from 300 to 200 ka. The lava flows crop out
along the inner caldera walls and can be subdivided
into leucite-bearing and sanidine-bearing groups.
The leucite-bearing lavas show chemical and
mineralogical characteristics typical of HKS rocks,
whereas the sanidine-bearing lavas are generally
weakly silica under-saturated. From 200 to 100 ka a
main explosive activity gave rise to the emplacement
of several pyroclastic flows (third phase). The first
three ignimbrites (A, B and C; Locardi, 1965) show
a symmetric distribution around the caldera, whereas
the D Ignimbrite is only found on the W side (Figure
10).
The A Ignimbrite (Figure 12a, d) is characterized
by a basal plinian-fall deposit followed by three
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Figure 9 - Sketch map of the Cimino Volcanic District. a) Symbols: 1 = latitic lava;
2 = ignimbrites; 3 = collapsed lava dome; 4 = lava dome; 5 = Quaternary sediments;
6 = pyroclastic surges; 7 = lateral eruptive centres; 8 = olivine latitic lava.
b) Symbols: 1 = olivine latitic lava flow; 2 = latitic lava flow; 3 = 3rd cycle dome;
4 = 2nd cycle dome; 5 = 1st cycle dome; 6 = flow direction of the lower ignimbrite;
7 = boundary of the pyroclastic surge deposits;
8 = boundary of the upper ignimbrite; 9 = boundary of the lower ignimbrite.
flow units. Each flow unit is
formed, in proximal sectors,
by flattened, grey and black
scoriae in highly-welded,
ash-sized
matrix.
The
black scoriae are coarsegrained and contain leucite,
plagioclase, clinopyroxene,
sanidine and biotite crystals.
On the contrary, in the distal
sectors, lithification is caused
by zeolitization processes.
This ignimbrite is mainly
distributed in the W, E and
S sectors, with a maximum
thickness of about 10 m.
The B Ignimbrite begins
with a basal decimetric level
constituted by dark-grey
coarse ashes, uniformly
distributed around the VV.
This level consists of many
laminated ash layers showing
reverse or normal grading,
and it is overlaid by a plinian
pumice fall level. Three flow
units can be observed within
the ignimbrite body: the
basal one is characterized,
in the proximal areas, by a
“breccia” deposit made up by
coarse lithics with a diameter
up to 0.5 m. The subsequent
units show varying colours
and degrees of cohesiveness.
They are generally welded,
with flattened scoriae and
pumices included in a microscoriaceous, coarse-grained
matrix. Lithic fragments
are represented by subvolcanic rocks and sanidinebearing lavas; sanidine,
clinopyroxene, plagioclase,
olivine and biotite are also
present as loose crystals.
The C Ignimbrite is the
deposit with the largest
areal distribution in the VV
(Figure 11). It spreads out
symmetrically northwards,
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Figure 10 - Vico caldera evolution and areal distribution of the ignimbrites. Symbols: A = boundary of the A Ignimbrite;
B = boundary of the B Ignimbrite; C = boundary of the C Ignimbrite; D = boundary of the D Ignimbrite.
where it overlies the Vulsini pyroclastic deposits,
and southwards, where it is interbedded within the
Sabatini pyroclastic succession (Figure 12). It is
the most studied of the Vico ignimbrites (Locardi,
1965; Mattias and Ventriglia, 1970; Bertagnini and
Sbrana, 1986; Perini et al, 1997; Nappi et al., 2003).
At the base of the C Ignimbrite there is a metric
horizon made up by white plinian pumices. The
pumices are micro-vesiculated and contain sanidine,
clinopyroxene, biotite and rare hauyne crystals.
Three pumice flow units, from decimetric (the lower
two) to metric (the upper one) in thickness, follow.
The matrix consists of pale-grey ashes, containing
rounded sub-aphiric pumices. A lag-breccia deposit,
with scarce matrix and a maximum thickness of 20
meters in the proximal sector, follows. Towards the
distal sectors its thickness decreases abruptly and
the matrix appears to be constituted by coarse lapilli.
Lithics are represented by lavas, clay fragments and
thermo-metamorphic rocks. The sequence goes on
with a massive, welded deposit constituted by upto-metric flattened scoriae, followed by a sillar-type
deposit, with a zeolitized matrix containing large, and
rare, grey, rounded pumices.
The D Ignimbrite extends mainly in the eastern sector
of the VV (Figure 10); it appears as a massive, pale
grey or yellow deposit. The depositional sequence is
composed of many flow units: a fine-ash lithified level
at the base, followed by several flow units with a sharp
hydromagmatic character. The basal units are mainly
constituted by inverse graded levels, and contain
pomiceous lapilli, white coarse-pumices and rare
lithics in a micropomiceous or ashy matrix. Massive
deposits with a lithified ash matrix containing white
pumices, flattened dark pumices and heterogeneous
lithic fragments (obsidian fragments are also present),
occur as we move upwards. The final units include
at least four flow units: they are represented by palegrey or white deposits, containing white pumices,
obsidian fragments, leucitic lavas and sedimentary
fragments in an ash or micropomiceous matrix. These
units are massive in the proximal areas, and stratified
with reversely-graded layers in the distal sectors. A
fine-ash level occurs at the top.
2.4 Emplacement mechanisms of ignimbrites:
some examples in the visited area
Pyroclastic flow deposits from the Quaternary
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volcanism of Central Italy can be ascribed to a
broad spectrum of both eruptive and depositional
processes. The study of the mechanisms that regulate
the transport and deposition of pyroclastic flows has
dominated volcanic literature in the last few decades
(Sparks, 1976; Wright and Walker, 1981; Fisher,
1986, 1990; Valentine, 1987; Carey, 1991; Branney
and Kokelaar, 1992, 1997; Kneller and Branney,
1995; Palladino and Valentine, 1995; Druitt, 1998;
Freundt and Bursik, 1998; Valentine and Fisher, 2000;
Capaccioni et al., 2001; Palladino and Simei, 2002;
Valentini, 2002, 2003). Though numerous authors
have tried to shed light on this topic, today it still
remains unclear because proposed models are often
different and ill-matched.
Several authors (Sparks, 1976; Wright and Walker,
1981; Fisher, 1986; Valentine and Fisher, 1986;
Valentine, 1987; Carey, 1991; Palladino and Valentine,
1995) believe that pyroclastic flows are partly- or
non-fluidized, highly-concentrated density currents
that move in a laminar and/or plug style, and stop “en
masse” along all the flow body. According to Valentine
(1987) and Fisher (1990), transport and deposition
systems are one and the same. The highest velocity
gradient and shear stress occur in the basal portion of
the flow, while almost constant vertical flow velocities
(“plug” zone) occur in the upper portion (Palladino
and Valentine, 1995). Deposition takes place when
the applied shear stress becomes lower than the yield
strength of the material. The resulting deposit is then
represented by a massive unit with possible shearinduced inverse size-grading at the base (layer 2a;
Sparks, 1976), and density-induced normal grading
at the top (layer 2b; Sparks, 1976). Therefore, these
features are considered strong evidence for deposition
from concentrated suspensions (Druitt, 1998).
An alternative model, already envisaged by Fisher
(1966), was proposed by Branney and Kokelaar
(1992). In agreement with the depositional model
Figure 11 - Vico Volcano: areal distribution
of the C Ignimbrite.
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Figure 12 - a) = Vetralla: Vico Volcano, A Ignimbrite.
b) = Pitigliano: Vulsini Volcanic District, e Ignimbrite
underlying the E Ignimbrite. c) = Sovana Necropolis:
“Via Cava” of Cavone, excavated inside the C Ignimbrite,
d) = Vetralla: Vico Volcano, matrix of the
A Ignimbrite: detail of photo (a).
of the high-density turbidity current (Lowe, 1982),
the authors suggest that pyroclastic flows can be
considered as sustained and stratified flows which
deposit at the base by progressive aggradation. The
depositional system is restricted to the basal part of the
flow, where the high particle concentration suppresses
turbulence, independently and with different rheology
from the overriding, more diluted and turbulent
transport system. This is also in accordance with the
high-velocity, turbulent pyroclastic flow end-member
proposed by Palladino and Valentine (1995). In the
sustained and stratified flows, the basal zone moves
like a shear-induced grain flow, just before deposition
by frictional freezing. The basal depositional system
is composed of a granular flow zone subdivided
into a lower portion in “frictional regime”, where
particles glide along each other, passing upwards
to a portion in “collisional regime”, where particle-
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possible normal grading for lithic and inverse for
pumice clasts, overlaying a fine-grained, inversely
graded basal layer. These flows emplace by “en
masse“ freezing up as the shear rate drops below
the yield strength throughout the entire flow height
(Sparks, 1976) or by rapid stacking of flow laminae
from bottom up (Palladino and Valentine, 1995).
Analysis of structural and textural properties of
pyroclastic flow deposits takes on major importance
for investigating the genetic mechanisms of deposits.
Accordingly, Palladino and Simei (2002) propose
facies analysis as the main distinguishing criteria
in pyroclastic deposits. The authors indicate, as
examples of type 1 deposits in the Vulsini area, part
of the basal layer of the “C Ignimbrite” (Sparks,
1976) of the Latera Volcanic Zone (or “Sovana
Eruption Unit”; Vezzoli et al., 1987; Palladino and
Taddeucci, 1998), and the coarse lithic breccias with
the associated spatter flow deposits of the “Onano
eruption succession” (Marsella et al., 1987). The
type 2 deposit is well represented in the “OrvietoBagnoregio Ignimbrite” (Nappi et al., 1994b) of
the Bolsena Volcanic Zone. Finally, the authors
interpreted much of the Latera ignimbrites as derived
from type 3 pyroclastic currents.
Although facies analysis represents the main tool for
discriminating between different types of pyroclastic
deposits, we believe that it should be supported
by other investigative methods. The intensive
secondary mineralization that very often affects the
ash-sized matrix, and also the superficial alteration,
hide structures and textures. Moreover, the lack of
traction-induced structures and grading, according
to Kneller and Branney (1995), may not only be
related with “en masse” deposition, but also with a
gradual transition between transport and depositional
systems. Massive deposits may, in fact, also originate
from progressive aggradation of basal depositional
layers (Branney and Kokelaar, 1992), in which the
residence time of particles under shear conditions
(which ultimately depends on sedimentation rate)
is not enough to produce grading, dunes or ripples,
but, rather, enough to produce directional fabric.
A continuous incremental deposition at the base
of a pyroclastic current could then produce, under
different conditions, massive beds or layered flow
units (Capaccioni et al., 2001; Valentini, 2002, 2003).
A careful evaluation of the qualitative and quantitative
information about the directional fabric may, therefore,
help shed light on the emplacement of ignimbrites
(Branney and Kokelaar, 1992). Several fabric studies
particle collisions prevail (Freundt and Bursik, 1998).
Before deposition, dispersive pressures due to grainto-grain frictional and collisional interactions develop
inverse size-grading and directional fabric (Rees,
1968). According to Kneller and Branney (1995),
the absence of traction-induced structures, together
with the development of a poor fabric, result from the
occurrence of a gradual transition between transport
and depositional system. Otherwise, structures
would occur distinctly and a good fabric would
develop. Hence, massive beds or layered flow units in
ignimbrites may represent the result of a continuous
incremental deposition at the base of the flow.
The debate on transport and depositional mechanisms
of ignimbrites should now be considered within the
framework of the controversy over the distinction
between “surge” and “flow” deposits. The concept
of these two respective modes of transport as two
fundamentally distinct phenomena is eclipsed by the
idea that they might represent two end-members of a
variable spectrum of possible particle concentrations
in between (Wilson and Houghton, 2000).
Accordingly, the two end-members are correctly
represented in the recently-proposed terms “highor low-concentration pyroclastic density currents”
(Valentine and Fisher, 2000).
In a recent paper by Palladino and Simei (2002),
three flow scenarios and corresponding deposits have
been identified, within the continuum of pyroclastic
currents ranging from diluted to concentrated end
members, based on a survey of pyroclastic successions
in the Vulsini Volcanic District.
The first is represented by diluted, turbulent
pyroclastic currents producing normally or multiple
graded beds, for progressive aggradation during the
passage of the flow due to direct fallout from the
gas-pyroclast suspension. The related deposits are
massive to planar/cross laminated, with no fabric
development, but a possible clast imbrication.
The second can be represented by density-stratified
pyroclastic currents with a concentrated bed-load
region, beneath a turbulent, diluted and fine-grained
upper part, depositing inversely graded beds by
traction carpet sedimentation. Diffuse beddingparallel clast fabric and other traction features, such
as laterally discontinuous trains of clasts, lamination
and local imbrication of elongate clasts, are indicative
of laminar shear prior to deposition.
The last scenario is represented by self-sustained,
high particle concentration, laminar, mass flows
developing massive, meter-thick deposits with a
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in pyroclastic flow deposits have been carried out
measuring the orientation of single elongate clasts
(Elston and Smith, 1970; Suzuki and Ui, 1982, 1983;
Kamata and Mimura, 1983; Potter and Oberthal,
1987; Ui et al., 1989; Hughes and Druitt, 1998).
Anisotropy of magnetic susceptibility has also been
used as a fabric indicator in ignimbrites (Ellwood,
1982; MacDonald and Palmer, 1990; Hillhouse and
Weels, 1991; Seaman et al., 1991; Fisher et al., 1993;
Baer et al., 1997; Cagnoli and Tarling, 1997).
Data regarding directional fabric obtained by using
a computer-assisted image analysis method from
different ignimbrites (Capaccioni and Sarocchi, 1996;
Capaccioni et al., 1997; Capaccioni et al., 2001;
Valentini, 2002, 2003) have recently been presented
and discussed to make inferences on the emplacement
processes of pyroclastic currents. The analytical
method consists of a computer-aided image analysis
system, able to carry out textural investigation
(grain size analysis, morphological analysis and
direction of lengthened particles) on consolidated and
unconsolidated rocks, at different scales. Details of
this method are described by Capaccioni et al. (1997).
Orientation data are processed to obtain information
about the occurrence of preferred particle orientations
and their strengths. Specific statistics are used in order
to gather information on the occurrence of anisotropic
distributions, unimodality or multimodality of
the circular frequency distributions, degree of
concentration of measures around the mean direction
and, finally, confidence angles of the mean direction
(Capaccioni et al., 1997).
Fabric data of some pyroclastic flow deposits from
the Vulsini and Cimini Volcanic Districts have been
obtained by using the described image analysis
method, and their relative transport and depositional
mechanisms have been interpreted. Samples were
collected vertically at metric intervals of up two
sections through each deposit. Where it was possible
the analysed sections were selected along the same
paleovalleys, at different distances from the source
area.
The “Orvieto-Bagnoregio Ignimbrite” (from VVD)
and “C Ignimbrite” (from VV) are not-welded but
lithified due to secondary mineralization. They have
similar depositional sequences and the geometries of
their deposits are also similar. They show both vertical
fluctuations in the mean particle orientation values
of about ±60°, and large variations in the strength
of particle iso-orientation with height. The circular
frequency distributions of particle orientations are
almost always anisotropic and unimodal, in line with
a theoretical Von Mises distribution (the circular
equivalent of a unimodal, log-normal distribution)
(Capaccioni et al., 2001; Valentini, 2002, 2003).
In contrast, the welded “Cimina Ignimbrite” (from
CVD) shows vertical homogeneities in mean
orientation values with height, and generally lower
degrees of anisotropy. The circular frequency
distributions of particle orientations are almost always
anisotropic and unimodal, with cases of isotropic or
polimodal distributions as well. A parallel-to-flow
iso-orientation is present in the unimodal samples,
whereas the polimodal distributions show two main
modes. One is placed parallel-to-flow, the other
transverse-to-flow. Detailed analysis of these samples
has shown the link between sizes and shapes of
the clasts, and the direction of the iso-orientation
obtained (Capaccioni et al., 2001; Valentini, 2002),
in accordance with some models proposed in the
literature (Lindsay, 1968; Best, 1992).
Such differences have been interpreted as being
the results of different depositional mechanisms:
(a) incremental deposition at the base of a densitystratified, partially turbulent flow for the “OrvietoBagnoregio Ignimbrite” and the Vico “C Ignimbrite”,
and (b) “en masse” deposition of a viscous-dominated
laminar mass flow for the “Cimina Ignimbrite”. In the
former case, during transport, particles under solidus
temperature are subjected to a frictional regime,
as well as gliding and dispersive pressures, which
eventually produce size-inverse grading and variable
degrees of iso-orientation.
The iso-orientation varies according to the residence
time of particles in the basal shear conditions. In the
case of the Cimina Ignimbrite (VVD), elongated
particles, supported in a laminar flowing viscous
matrix, undergo periodic motions which tend to
develop parallel-to-flow iso-orientation. Fabric data
in the deposit suggest a general vertical homogeneity
of the rheological properties of the flow and only rare
plug horizons.
In addition, analyses in progress on the Latera D
Ignimbrite, combined with its textural and structural
features, allow us to interpret the mechanism for
incremental deposition at the base of a densitystratified and partially-turbulent flow, as the possible
depositional mechanism of much of this deposit. On
the contrary, textural data obtained through image
analysis on the “Nenfro Ignimbrite” (VVD) better
agree with an “en masse” deposition from a laminar
mass flow.
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2.5.1 The Etruscan tombs of Sovana
The area surrounding Sovana was one of the most
important Etruscan centres, whose earliest settlements
date back to the 8th century B.C. It remained an
channels, huge chiselled rocks and sculptures are
so common as to make this area unique in terms
of the quality and quantity of its great excavated
works. Indeed, Sovana is also called “The City and
Civilization of Tufa”.
The most important tombs of Sovana are located
along the “Folonia”, “Calesine” and “Picciolana”
valleys, inlaid from the homonymous streams. Two
main types can be distinguished: (1) the dado (cubic),
semi-dado and false dado tombs, and (2) the niche and
the temple tombs.
The first type, which is the most common, can be
considered a more highly evolved version of the
ancient, simple dado type, already known in southern
Etruscan towns (Figure 13). A substantial enrichment
with decorative architectural elements, and the
relocation of the funeral room to the lower level of
the tomb, are the main changes. A false carved door,
which symbolizes the entrance to the world beyond
the grave, was placed in front of the dado. The funeral
room containing the mortal remains, located under
the dado, was accessible through a long, deep open
Bulk
density
(γ) g/cmc
Apparent
density
(γs) g/cmc
Porosity
(P) %
* Compressive
* Tensile
Sample
strength
(σf) Mpa
strength
(σf) Mpa
§
Compressive
strength
(σf) Mpa
§ Tensile
strength
(σf) Mpa
1
1.19
2.52
53
44
7.2
40
6.5
2
1.34
2.45
45
68
9.0
46
5.6
3
1.07
2.52
57
28
4.5
22
4.5
4
1.07
2.38
55
25
4.1
22
-
5
1.36
2.25
39
105
11.8
78
9.5
6
1.32
2.48
47
52
7.8
42
-
7
2.11
2.63
20
214
21.6
-
-
Table 2 - Mean values of mechanical and physical parameters of pyroclastic flow deposits from the Vulsini (1-6)
and Cimini (7) Volcanic Districts: 1) Nenfro Ignimbrite; 2) the Orvieto-Bagnoregio Ignimbrite distal quarry;
3) Orvieto-Bagnoregio Ignimbrite at Orvieto town (Manfredini et al., 1980); 4) Latera C Ignimbrite;
5) the Latera D Ignimbrite distal quarry; 6) the Latera D Ignimbrite proximal quarry;
7) Cimina Ignimbrite. Symbols: * dry samples; § saturated samples.
important centre during the whole Etruscan period, up
to the Roman civilization (Bianchi Bandinelli, 1929;
De Feo, 1993, 2001).
The pyroclastic successions of Sovana were
thoroughly worked during this entire period. Tombs,
necropolises, sacred pathways, wells, drainage
2.5 Use of the ignimbrites
Up to the Prehistoric Age the ignimbrites of Latium
were used as living caves. The Etruscans and Romans
then used them to make tombs, monuments, temples
and amphitheatres. Today, they are used for walls or
insulation and sound-proofing. Their mechanical and
physical characteristics seem to be related both to
their structure and to the lithification process that the
deposit underwent. Apparent density, bulk density and
porosity, as well as compressive and tensile strength,
on naturally dry and saturated samples were measured
on Nenfro, Orvieto-Bagnoregio Ignimbrite, Latera C
and D Ignimbrites. Uni-axial compression tests have
been carried out on cylindrical samples with H = 2D.
Tensile strength was measured by using the indirect
Brasilian test. A summary of these results is shown
in Table 2.
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passage (dromos). The sepulchral monument appears
to be composed of two parts: a cubic block jutting
out from the rock wall with a false door and moulded
crowning; a small rectangular over-structure, called an
“altar-bring cippus”, also decorated with a moulding.
The variegated, monumental tombs of the second
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Figure 13 - Sepulchral monument types: a) dado (cubic), semi-dado and false dado tombs; b) temple-style tomb.
type are more elaborate than those in the southern
Etruscan, rupestrian necropolises. Sovana, in fact,
is considered one of the most thriving centers for
the elaboration of architectonic shapes in funerary
art. The shrine tombs, with their underlying funeral
room, can consist of a simple empty tympanum,
without decorations (for example, the group of tombs
located at the top of “Poggio Stanziale”), or, as in the
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Figure 14 - a) Boundary wall of the town of Pitigliano, which is built on top of the complete series of the Vulsinian
ignimbrites. b) Necropolis of Sovana, the Tomba Pola Temple. c) Sutri, Roman amphitheatre.
d) Necropolis of Sovana, the Tomba Ildebranda funeral room
case of the “Tomba del Tifone”, they can be painted
with symbolic decorations. In some cases the front
of the tomb looks as if it was composed of columns,
assuming the architectural character of a temple (e.g.,
“Tomba Ildebranda”, “Tomba Pola”; Figure 13b); a
circular plan with a columned front can be found at
“Tomba del Sileno”.
Other monuments have a more complex structure,
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with an image of the deceased lying on a funerary
bed, located on the floor of the rectangular room or
vaulted niche, under the tympanum between the two
doorjams of the shrine (e.g.,“Tomba Siena”, “Tomba
della Sirena”). A vaulted niche also appears in some
smaller tombs at “Poggio Stanziale” and “Poggio
Grezzano”, where the image of the deceased is
replaced by a false door.
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Figure 15 - Representative stratigraphic sections of the
OBI pyroclastic sequence (modified from Nappi et al.,
1994b). PF = pumice fall; GS = ground surge deposit;
L1 =”layer 1” deposit; JD = jetted deposit;
AF= co-ignimbrite ash fall.
Field trip itinerary
DAY 1
(from Florence to Bolsena)
Stop 1.1:
Orvieto
Starting from the railway station parking lot, we will
walk up to the cable car station. We will then cross
the sillar facies of the Orvieto-Bagnoregio Ignimbrite
(OBI) in a cable car, arriving at the panoramic terrace
where the “Pozzo di San Patrizio” is located (Santini,
1995).
The OBI is at its maximum thickness of 60 m
(Figure 15, log 10) at Orvieto. The main body of the
ignimbrite is a reddish sillar-type deposit, generally
strongly zeolitized, containing analcimized leucitebearing black pumices, from which the Italian name
of “Tufo rosso a scorie nere” derives. In this area
only the uppermost unit is present; the most abundant
facies is represented by a lithified massive deposit,
whereas a loose facies occurs only at the “Bardano”
outcrop. The juvenile fragments are made up by black
glassy pumices, containing large analcimized leucite
crystals, with devitrified structures. The pale to grey
pumices are rare and show a porphiritic structure with
sanidine crystals in a generally fine-grained matrix
(Nappi et al., 1994b).
Most of the town of Orvieto (Santini, 1995) spreads
out across a small ignimbritic plateau. The pyroclastic
flow deposit, easily quarried and shaped according
to the requirements of the area’s inhabitants, is the
material from which the town’s houses and buildings
have been built. A network of caves has been tunnelled
into the ignimbrite. Wells, cisterns and large caves for
pressing olives and grapes were excavated during the
Middle Age.
The most important well in the town is the “Pozzo di
San Patrizio”, one of Orvieto’s main attractions. The
well was ordered by Pope Clemente VII to ensure a
water supply in the event of the town being besieged.
The architect “Antonio from San Gallo the Younger”
was commissioned to do the work, which began in
1528. The well has attracted many curious visitors,
ever since it was re-opened in 1956. It is about 62 m
deep and 13.40 m wide. It is circular, with a series
of two diametrically-opposed doors, which lead into
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two concentric spiral staircases independent from
each other and non-communicating. Each stairway
has 248 steps, which are easy to descend for packanimals. The excavation extends through the OBI to
the Tertiary clay.
pumices and rare lithic fragments, is present at the top
of the sequence.
Stop 1.2:
Stop 2.1:
Civita di Bagnoregio
We will leave the town via the steep walls which
encircle Orvieto’s entire eastern sector, where the
works of rock-consolidation can be observed. We will
then move southwards, climbing the old lava flows
which border the Bolsena caldera. Then, moving
across the OBI plateau, we will arrive at Bagnoregio.
We will pass through the entire village moving
eastwards and, finally, descending to the bridge of
Civita di Bagnoregio.
Here the OBI is mainly represented by the upper
unit with sillar-type facies (Figure 15, log 6). The
lower part is constituted by decimetric ash levels
with reversely-graded pumices. A fine-grained ash
bed with travertine deposits is present at the base.
The town of “Civita di Bagnoregio” was developed
on (and partially inside) the sillar-type facies of the
OBI. Ignimbrite overlies all the pyroclastic deposits
of the Paleobolsena and Bolsena Volcanic Zones from
the older plinian fall deposit (Basal Pumices, 576 ka;
Nappi et al., 1994a) to the basal plinian deposit of the
OBI (333 ka; Nappi et al., 1994b).
Montefiascone
We are located along the Montefiascone caldera
rim on a spatter-cone that arose after the formation
of the caldera. A scoria quarry, related to the final
circumcalderic strombolian and hydromagmatic
activities, can be observed. The Martana and
Bisentina Islands, which are visible in front of us,
represent the final sub-lacustrine activity of the
Bolsena District. The Martana Island is a surtseyan
tuff-cone; the Bisentina Island is also of surtseyan
origin, but followed by final effusive activity.
“Pidocchio” Spring
Leaving Bagnoregio we will take the road for
Lubriano, traveling north-east for about 1.5 km, until
we get to “Pidocchio” spring. Both the zeolitized
and the loose facies of the upper unit of the OBI are
present in this outcrop (Figure 15, log 5). The lower
unit of the pyroclastic deposit appears to be composed
of multiple, inversely-graded pumice layers.
Stop 1.4:
Bolsena town, the “Giglio” Convent
This is one of the most proximal outcrops of the OBI
(Figure 15, log 1). At the bottom of the sequence we
can observe a plinian fall deposit that is pedogenized
and shows its maximum thickness. It is overlain by a
basal, fine-grained, slightly-laminated, crystal-rich ash
layer. We then find multiple ash levels with inverselygraded white pumices, which become a coherent ash
–deposit, rich in lithic fragments and white pumices
in the upper part. A final unit, composed of black
DAY 2
(from Bolsena to Sovana)
Stop 2.2:
Pitigliano
The succession observable in this outcrop (Figure 16)
includes most of the Latera ignimbrites in their typical
facies. The lower and the upper Latera ignimbrites
(A and F; Sparks, 1975) are not present here; the A
Ignimbrite, however, can be observed during the visit
to the Ildebranda Tomb (stop 2.3).
Following the succession from the top to the bottom,
the first sillar-type deposit is represented by the E
Ignimbrite (Sparks, 1975). It is a 15-m-thick deposit,
probably constituted by more than one flow unit, which
are not clearly visible here. The intense zeolitization
which affects the ash-sized matrix, in fact, obliterates
the flow units. The matrix contains tabular-shaped, pale
and black pumices, with subordinate, heterogeneous
lithic fragments. Consolidated and laminated lightyellow ashes with tree holes are present at the base,
underlain by a lithified ash bed (basal surge). The
underlying e Ignimbrite (Sparks, 1975) appears to
be constituted by reverse-graded multiple layers of
light-grey fine ashes with accretionary lapilli. At the
bottom, four decimetric ash layers with tree holes
are present. Because of the presence of tree holes
at their base, the E and e Ignimbrites have often
been confused with one another. The lower deposit
is represented by Sparks’ (1975) D Ignimbrite or
Vezzoli et al.’s (1987) “Sorano Formation” of. It is
one of the most widely used building materials, as
evidenced by the many quarries in this ignimbrite
in the northern Vulsini District. In this outcrop the
D Ignimbrite appears to be un-consolidated and it
Stop 1.3:
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Leader: G. Nappi
Simei (2002) have related this level to direct fallout
from the gas-pyroclastic suspension, with or without a
late clast-by-clast tractional stage. The lowest deposit
of the Latera succession corresponds to Sparks’
(1975) B Ignimbrite, which is formed by multiple,
fine-grained ash levels with accretionary lapilli and
large lithic fragments. At the base there is a 40 cm
thick pumice fall level. The e, D and B Ignimbrites,
being constituted by a repetition of beds, often
inversely-graded and showing traction features, may
be correlated to Palladino and Simei’s (2002) type 2
deposits. On the contrary, the E and C Ignimbrites, with
their massive, poorly-sorted main bodies, correlate to
the type 3 deposits. Below this, a travertine ash-layer,
underlain by a meter thick pyroclastic flow deposit,
can be observed. This pyroclastic deposit may be
referred to the oldest Vulsini ignimbrite (the Nenfro
Ignimbrite) related to the Paleobolsena activity. An
ash deposit with accretionary lapilli can be observed
at the base of the sequence.
Stop 2.3:
Figure 16 - Stratigraphic succession of the Vulsinian
ignimbrites near the town of Pitigliano.
is composed by multiple, fine-grained ash layers
with centimetric rounded pumices. The underlying
C Ignimbrite (Sparks, 1975), often represented by
a coherent sillar-type facies, was the most widely
used deposit in Etruscan times, and into which tombs
were bored. In this outcrop, the pyroclastic deposit
is mostly composed of black pumices containing
analcimized leucite crystals in a loose brown matrix,
with a base enriched in lithic fragments. At the base
this ignimbrite always shows a pale-yellow ash bed
(which in this outcrop is 40 cm thick) enclosing grey
pumice clasts and accretionary lapilli. Palladino and
Sovana
The first sporadic settlements in Sovana date back to
the Neolithic and Bronze Ages. Indeed, archeological
excavations have confirmed that in this early period an
inhabited center already existed. At the beginning of
the Iron Age these centers were suddenly abandoned,
to be later re-occupied by the Etruscans, starting from
the 9th – 8th centuries B.C. (Figure 17).
The Etruscan “Suana” or “Suama” was an important
center, from both a commercial and cultural standpoint.
Sovana reached its maximum size around the 4th
– 3rd centuries B.C., as evidenced by the monumental
necropolis attributed to this period, and it remained an
important center even during the Roman colonization.
The number of Etruscan inscriptions from the Roman
period, in fact, reveal that the national language and
culture still existed.
By the 4th century A.D., Sovana was the seat of the
local Bishopry and in 935 A.D. the town was chosen
by the “Aldobrandeschi” counts as the capital of
their country. This area was also chosen as a refuge
by hermits and ascetics (there are some examples
of these hermit caves in Sovana), thus contributing
to the spread of Christianity. Moreover, Sovana was
the birthplace of Pope Gregorio VII, born in the 11th
century.
His name, “Ildebrando di Sovana”, suggests there
might be a relationship with the Aldobrandeschi
family. In 1312 the city became a property of the
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Orsini family, which maintained control until 1410,
when it was occupied by the army of the Sienese
Republic. From this moment onwards, Sovana began
its slow decline, sinking into a state of total abandon
and ruin. Only its recent rediscovery breathed new
life into the town after centuries of neglect (Bianchi
Bandinelli, 1929; De Feo, 1993, 2001).
Sovana’s most spectacular monument is its beautiful
cathedral. Dedicated to the Apostle Saint Peter, it
is a rare example of a church in Romanesque and
Gothic styles. The cathedral was probably built on the
first, original site of the Etruscan acropolis; it would
seem to be the oldest area, dating back to the earliest
settlements, because of its position on the highest and
best-defended point in Sovana.
The walls, arches and cupolas of the cathedral were
built using blocks quarried from the local ignimbritic
outcrops. The building’s walls were constructed using
the Latera C Ignimbrite (an orange sillar-type deposit
with black pumices); the supporting arches were
built using the Latera D and E Ignimbrites, while
most of the sculptures were carved in the Latera D
Ignimbrite.
This cathedral is unique for the excellence of
its sculptured decorations and the harmonious
architecture of its interior. The original structure of
the building probably dates back to the 9th century,
through it owes its current appearance to work carried
out between the 12th and the 14th century.
The marble doorway, with its decorations executed in
Gothic style, is perhaps the most remarkable element
of the cathedral. The portal consists of an external
arch, with a sculpture of the human spirit on the
upper part and two lion heads in the middle section.
Sculptures with various symbolic motifs (a mermaid,
a human figure, two peacocks, a rose, a warrior and
some geometric motifs) are found in the lower part.
A second internal arch is formed by two columns
decorated with a spiral design. The innermost part of
the portal is decorated with symbolic motifs, such as
flowers (symbols of the unfolding of life) and spirals
(a symbol of life and all-pervading energy). All these
symbols, found all over the external walls of the
church as well, predate Christianity.
The internal part of the cathedral is divided into three
principal naves. The bones of Saint Massimiliano,
the Patron of Sovana, are contained above the altar
on the left aisle. The sculptures on the upper section
of the columns’ capitals, representing biblical scenes
and attributed to the 11th century Lombard school, are
considered very important. Other important works
include the baptismal font of engraved travertine
from 1434, and the 17th century canvas, by Domenico
Manenti, representing the Martyrdom of Saint Peter
(De Feo, 2001).
Stop 2.4:
Figure 17 - Ancient Etruscan footpaths around Sovana.
P09
The necropolis of Folonia valley
This necropolis is located along the way to “San
Martino sul Fiora”, heading towards Saturnia. It was
discovered in the 1850s, but excavations started in
1920. The entire necropolis is set within the Latera
C Ignimbrite and the underlying pomiceous deposits.
The monuments of the tombs are engraved in the C
Ignimbrite, while the funerary rooms containing the
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Leader: G. Nappi
mortal remains were excavated within the mainly
pomiceous, reworked, pyroclastic deposits, below the
basal ash level of the C Ignimbrite.
At the beginning of the necropolis we find the
openings of two great paths. One of them is closed,
but the other (the spectacular “Via Cava of San
Sebastiano”) can be walked on. This Etruscan road
is about five hundred meters in length, with twentyfive-meter high walls. There are several incisions,
often unreadable, high up on the walls. Halfway along
the road, there is a deviation to the top of the path,
where there are several small chamber tombs. Two
of these chambers were used in the Middle Ages as
shelters for hermits during the early Christian period:
several incisions of Christian crosses are visible on
the walls. Ancient tombs, which date back to the 7th
century B.C., are also located at the beginning of the
necropolis. Numerous other tombs, dating from the
7th to the 2nd century B.C., can be found along the
valley. Along the necropolis we find a series of wellpreserved façade tombs, also dating back to the 3rd
century B.C.. The top of the tombs, used for sacrifices
and offerings, can be reached by lateral steps; on the
front of the tombs, carvings representing the entrance
to the afterlife are visible. The names of the dead are
also engraved on these tombs.
Further into the necropolis we find the famous
“Tomba della Sirena”, which dates back to the 3rd
century B.C. and is one of the major examples of
Etruscan work in the Hellenic style. This large nichetype monument is an arch hewn from a single rock
mass. A double tailed mermaid, which symbolizes the
Sea Goddess and the afterlife, is carved on the front.
In addition, a figure lying on the funeral bed, with the
inscription of a woman’s name over it, is carved on
the inside of the arc. On both sides of the monument
are sculpted figures representing protective spirits of
the tomb. The small room with funerary beds, below
the facade, can be reached through a narrow passage
(Fiocchi and Nicolai, 1988; De Feo, 1993, 2001).
The Ildebranda tomb represents one of the most
important examples of Etruscan stone architecture,
and the only exstant, well-preserved Etruscan temple
tomb. It was discovered in the 1920s and dates back
to the 3rd century B.C. The front of the tomb rests on
twelve columns (perhaps corresponding to the twelve
capital towns of Etruria). Many floral decorations and
sacred animals were carved on the tympanum of the
temple. Along the cornice of the tympanum, several
complex figures, some of which are probably related
to the zodiac, can be seen. Two funerary corridors lie
below the temple. The main one leads down to the
center of the temple to a cruciform funeral chamber.
The lateral corridor leads to a chamber thought to be
even older (4th century B.C.). Its ceiling is carved
with concentric squares, reproducing the ceiling of
an Etruscan house, and several funerary beds are set
along the walls.
There are also two recently-discovered, niche tombs
between broad stairways. One of the tombs depicts
the front of the temple while two sculpted lions guard
the entrance to the other tomb. Excavation here is still
in progress and these tombs cannot be visited (De
Feo, 2001).
Not far from the Ildebranda Tomb, near a group of
recently-discovered tombs, lies the Pola Tomb. It is
a huge rock whose face was carved into the shape
of a temple (eight columns supporting a decorative
tympanum). The tomb dates back to the 3rd century
B.C. Below the temple, a deep, long corridor leads to
a cruciform burial chamber.
Below the high cliff of “Poggio Stanziale”, in front
of the Ildebranda tomb, stands a group of façade
tombs. One of these is the Tifone Tomb, a fine
Hellenistic monument of the 2nd century B.C.. The
name of this niche tomb derives from the sculpture
on the tympanum of the façade, representing the
mythological “Tifone” (typhoon), the sea monster
symbolizing the Ocean and the afterlife, from whose
mouth blew the terrifying winds of the tempest.
Lateral steps lead up to the top of the tomb, where
funeral rites were celebrated. Some corridors, one of
which leading to the funerary chamber, lie under the
monument.
The Cavone is a huge Etruscan passage located
beneath the Ildebranda Tomb. Moving beyond the
entrance, high up along the top of the passage, we find
several burial chambers, some of which were lived
in by hermits during the Middle Ages. Remains of a
fresco of the Madonna and Child in a carved niche
can be seen. Several incisions, visible on the walls
of the Cavone, are ascribable to different periods,
including Roman and Christian eras, as evidenced
by several crosses. For this reason the Cavone was
named “Devil’s Road” and is still considered a cursed
place. About halfway down the passageway, an
Etruscan inscription (VERTNE) dated to the 4th - 3rd
centuries B.C., is visible. It was probably dedicated
to the Etruscan god, Vertumno or Veltha, while the
swastika near the inscription was a symbol of the Sun
and the Cardinal Points (Fiocchi and Nicolai, 1988;
De Feo, 2001).
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and orthopyroxene are also present. The average
phenocryst content is about 42%.
Stop 3.1:
Stop 3.3:
Vitorchiano quarry
Starting from the Orte-Viterbo freeway, 300 m on
the left heading towards Orte, we find the large
Vitorchiano quarry, within the Cimina Ignimbrite
(hereafter CI).
The CI (1.35-1.19 Ma; Lardini and Nappi, 1987)
extends radially around Mt. Cimino (Figure 9), and
it crops out across an area of about 40 km2, because
it is partially buried by the younger deposits from the
Vico Volcano. The magma-volume of the CI can be
estimated as being around 15 km3. The distribution
of the ignimbrite appears to be strongly influenced
by the paleo-topography, and it shows its maximum
thickness near the feeding vent, where drilling
recorded 150-200 m of depth (Micheluccini et al.,
1971). The deposit appears quite homogeneous
in its textural parameters, and massive along its
entire thickness. It is probably a multiple-ignimbrite
even if the number of the flow units is difficult to
evaluate. One flow unit, two meters thick, can be
observed at the top of this outcrop. The CI is a grey,
highly-welded deposit, which grades into a pink,
non-welded, pumiceous facies in the distal sectors.
The ash-sized matrix contains biotite, feldspar and
pyroxene crystals. In the welded zone, flattened
quartz-latitic pumice clasts and glassy shards define a
eutaxitic texture. The black “fiamme” are from a few
centimetres up to one meter in length, and from a few
millimetres to 3-4 cm thick. The sparse lithic clasts,
represented by sedimentary and lava-dome fragments,
do not provide any evidence of lateral size-grading.
The basal unit appears to be very rich in the lavadome fragments. Looking upwards some lithic-rich
zones are also visible, probably marking the base of
different flow units.
Capranica
Following the Cassia road, past the village of
Capranica, we will park on the left near the “Todis”
supermarket. We pass through a tunnel leading to the
“Forte delle rocce”; 300 m further along the road we
will find the series of the Vico ignimbrites (Figure
18). As regards the A Ignimbrite, only the upper part
of the deposit can be observed; it appears as a purple,
ash-sized matrix with analcimized leucite and biotite
crystals, with a lower part which is rich in lithic
fragments (marl, limestone and thermo-metamorphic
rocks), while the upper part is constituted by deeplypedogenized fine ashes. The pedogenized horizon is
covered by a loose, coarse, ash level, black in color,
showing cross and planar lamination. Several deposits
relate to the B Ignimbrite. First off, a light grey
pumice zone can be observed at the base. As we move
upwards this becomes a welded deposit containing
flattened black scoriae and rare lithics and pumice
clasts, which are sometimes concentrated in lenses.
Flattened black scoriae and large lithics contained in a
welded matrix are present at the top. The next deposit
(C Ignimbrite) begins with a basal plinian fall deposit
made up of subaphiric pumices, with rare sanidine
and clinopyroxene, and lithic fragments (sienite and
thermometamorphic rocks). The series continues with
multiple pumice flow units composed of a stratified
deposit of rounded pumices in fine ash matrix, about
2.5 m thick. On the upper part a breccia deposit, made
up by brown pumices, black scoriae with sanidine
and leucite, and large lithics (lava, clay and skarn
fragments), can be observed. The breccia horizon
is covered by a coarse-grained deposit of welded
and flattened black scoriae. This deposit grades
vertically to a sillar facies with large black scoriae
in a zeolitized, ash-sized matrix. The matrix shows
rounded microvesiculated grey pumices at the top of
the outcrop.
DAY 3
Stop 3.2:
Soriano nel Cimino lava dome
Many lava domes of different shapes and dimensions
formed in the central part of the Cimini Volcanic
District (Figure 9). This outcrop represents the
culmination, at different levels, of a single dome-mass
that has intruded into the Pliocene clay-substratum.
The surface of the dome is generally covered by large,
angular, and irregularly-shaped blocks. The occurrence
of large sanidine crystals is the constant characteristic
of the lava dome. Phenocrysts of plagioclase, biotite
Stop 3.4:
(from Bolsena to Rome)
P09
Sutri
The town of Sutri stands on a tufa spur, surrounded
by deep valleys with small streams, at the foot of
the Cimini (to the N-E) and Sabatini Mountains
(to the S-W). It is located along the ancient natural
passage between the southern Etruscan inland and the
coastal strip, as well as along the transit line between
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Leader: G. Nappi
Rome and the northern part of Latium. Thanks to its
strategic position, Sutri was an important center until
the late Middle Ages. Fragments of manufactured
objects found in this area have even been attributed to
the last phase of the Bronze Age (10th century B.C.),
bearing witness to the habitual visiting of this area as
early as the proto-historic age. Materials of impasto
used for habitations (attributed to the late final Bronze
Age) and remains of “pit tombs” and “small well
tombs” containing ceramic products (dating back to
the second half of the 8th century to the first decades
of the 7th century B.C.), were found at the La Ferriera
site, along the Cassia road about 3.5 km south-east
of Sutri. Remains of habitations from the Iron Age
were previously reported on Rocca Romana and the
Calvi Mountains, about 7 km south of Sutri; these
settlements died out during the 7th century B.C.
(Giuntella, 1980; Morselli, 1991).
The most famous monument in Sutri, the amphitheatre,
was unknown until the beginning of the last century.
The whole amphitheatre was excavated in the tufa
promontory which lies opposite the town. The inner
arena is elliptically-shaped, with a 49.6 m-long major
axis oriented NE-SW and a 40.8 m-long minor axis.
There are two wide underground passages with barrel
vaults at the end of the major axis. The entrance
facing the Cassia road is badly damaged, the entry
gallery with the upper tiers having almost entirely
collapsed. The arena is surrounded by a high podium,
which extends from the main entrances and separates
the arena from the “cavea”. Along the podium there
are ten doors located at regular intervals, five on each
side; they access a ringed walkway, which ends at the
main entrances.
The cavea is subdivided into three orders of stands,
and as many narrow corridors. The lower cavea can
be reached by a series of small steps, located along the
underground walkway, at the sides of the doors which
lead directly into the first enclosure. The middle
cavea could be accessed through four vomitoria (only
one, on the north side of the west gallery has been
preserved) excavated at the end of the two principal
entrances. On the walls of the vomitorium there are
the remains of a rainwater canalisation system, going
from the cavea to the outer side of the amphitheatre.
Eight small semicircular cavities, distributed at regular
intervals, are located in the middle cavea. A wide
rectangular niche, whose original configuration and
function are still unknown, is found in the central part
of the west side. The upper cavea is badly damaged.
At the top on the north-western side, there is a trumpet
Figure 18 - Stratigraphic succession of the Vico Volcano
ignimbrites near the town of Capranica.
vertically cut into the tufa bed. It is decorated with
semi-colons in relief and ends with a cornice. On the
opposite side this element is not present, because the
tufa bed is lower. Here the steps end in a wide corridor
that leads to the end of the outer perimeter. The
morphological features of the monument suggest that
it dates back to the period between the end of the 1st
century B.C. and the 1st century A.C. (Morselli, 1991).
The necropolis constitutes one of the most important
examples of Roman tombs in tufa. A number of the 64
tombs are actually visible in the tufa walls, distributed
on several levels. Already plundered in the early
Middle Ages, the tombs continued to deteriorate. The
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processes of the Pitigliano Formation (Latera Volcanic
Complex, Vulsini District, Italy). Acta Vulcanologica,
5, 31-39.
Capaccioni, B. and Sarocchi, D. (1996). Computerassisted image analysis on clast shape fabric from
the Orvieto-Bagnoregio ignimbrite (Vulsini District,
central Italy): implications on the emplacement
mechanisms. J. Volcanol. Geoth. Res., 70, 75-90.
Capaccioni, B., Valentini, L., Rocchi, M.B.L.,
Nappi, G. and Sarocchi, D. (1997). Image analysis
and circular statistics for shape-fabric analysis:
applications to lithified ignimbrites. Bull. Volcanol.,
58, 501-514.
Capaccioni, B., Nappi, G. and Valentini, L. (2001).
Directional fabric measurements: an investigative
approach to transport and depositional mechanisms
in pyroclastic flows. J. Volcanol. Geoth. Res., 107,
275-292.
Carey, S.N. (1991). Transport and deposition of tephra
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Stampa Alternativa.
De Feo, G. (2001). The hilltop towns of the Fiora
necropolis extends for about 150 meters along the
rupestrian front bordering the Cassia road.
Several tomb types can be recognized: one-room
tombs, double-room tombs, with or without an arch
opening, rectangular niches with or without a cinerary
urn cavity, arched niches. Both the cremation and
burial funeral rites were practiced in the necropolis.
Only one tomb was exclusively used for cremated
corpses, while the most frequent types are the mixed
rite tombs; three are only burial tombs.
The most important tombs are marked by carved
pediments on their outer sides, often with a rectangular
cavity where the inscription was made.
Two twin vaults lined with burial niches show more
elaborate decorations, with an arch set in the pediment
and simple sculptures at the outer corners. Remains
of painted stucco can be observed everywhere,
especially in the interiors; nevertheless, they are
not well-preserved, due to the numerous touchingsup which have occurred again and again since the
Middle Ages.
This necropolis is architecturally similar to other
monuments in the southern Etruscan area, in particular
in the countryside around Bomarzo (“Selva di
Malano”). The architectonic features, the prevalence
of cremation, the epigraphs carved in marble slabs,
suggest that the necropolis may date back to the same
period as the singular stone amphitheatre (Morselli,
1991), situated on the nearby hill.
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valley. A guide to the Etruscan and medieval centres
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from calcalkaline welded tuffs and paleomagnetic data
reliability from anisotropy of magnetic susceptibility
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flow direction of ryolitic ash-flow tuffs from fluidal
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pyroclastic surge across an area of high relief: the 18
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transport mechanisms. In “From Magma to Tephra:
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Gillot, P.Y., Nappi, G., Santi, P. and Renzulli, A.
(1991). Space-time evolution of the Vulsini Volcanic
Complexes, Central Italy. EUG VI, Strasburgo 24-28
Marzo, 1991, Terra Abstract, 3-1, 446.
Giuntella, A.M. (1980). Note per la topografia di
Sutri. Archeologia Laziale III, pp. 220.
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fabric, flow directions, and source area of the Lower
Miocene Peach Springs tuff in Arizona, California,
and Nevada. J. Geophys. Res., 96, 12443-12460.
Hughes, S.R. and Druitt, T.H. (1998). Particle fabric
in a small, type-2 ignimbrite flow unit (Laacher
See, Germany) and implications for emplacement
dynamics. Bull. Volcanol., 60, 125-136.
Kamata, H. and Mimura, K. (1983). Flow directions
inferred from imbrication in the Handa pyroclastic
flow deposit in Japan. Bull. Volcanol., 46, 277-282.
Kneller, B.C. and Branney, M.J. (1995). Sustained
high-density turbidity currents and the deposition of
thick massive sands. Sedimentology, 42, 607-616.
Lardini, D. and Nappi, G. (1987). I cicli eruttivi del
complesso Vulcanico Cimino. Rend. Soc. Ital. Petrol.,
42, 141-153.
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in mudflows. J. Sediment. Petrol., 38(4), 1242-1253.
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mediterranei: le ignimbriti del vulcano di Vico. Atti
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vulcanismo e bacini uraniferi nel Lazio. Relazioni e
Comunicazioni del 67° Congresso Soc. Geol. It., 30
pp.
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Depositional models with special reference to
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Sciotti, M. (1980). Problemi di stabilità della rupe di
Orvieto, XIV Convegno di Geotecnica, Firenze.
Marini, A. and Nappi, G. (1986). Origin and evolution
of the Montefiascone caldera (Vulsini Volcanoes).
Mem. Soc. Geol. Ital., 35, 657-665.
Marsella M., Palladino, D.M. and Trigila, R. (1987).
The Onano pyroclastic formation (Vulsini Volcanoes):
depositional features, distribution and eruptive
mechanisms. Period. Mineral., 56, 225-240.
MacDonald, W.D. and Palmer, H.C. (1990). Flow
directions in ash-flow tuffs: comparison of geological
and magnetic susceptibility measurements. Tshirege
member (upper Bandelier tuff). Valles caldera. New
Mexico, USA. Bull. Volcanol., 53, 45-59.
Mattias, P.P. and Ventriglia, V. (1970). La regione
vulcanica dei Monti Cimini e Sabatini. Mem. Soc.
Geol. Ital., 9, 331-384.
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alla geologia del Vulcano di Latera (Monti Vulsini,
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Micheluccini, M., Puxeddu, M. and Toro, B. (1971).
Rilevamento e studio geo-vulcanologico della regione
del Monte Cimino (Viterbo, Italia). Att. Soc. Tosc. Sc.
Nat. Mem. Serie a, 78, 301-327.
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Nicoletti, M. (1969). Datazioni argon potassio di
alcune vulcaniti delle regioni vulcaniche Cimina e
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basal ash deposit of the Sovana Eruption (Vulsini
Volcanoes, central Italy): the product of a dilute
pyroclastic density currents. J. Volcanol. Geotherm.
Res., 87, 233-254.
Palladino, D.M. and Valentine, G.A. (1995). Coarsetail vertical and lateral grading in pyroclastic flow
deposits of the Latera Volcanic Complex (Vulsini,
Central Italy): origin and implications for flow
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Palladino, D.M. and Simei, S. (2002). Three types of
pyroclastic currents and their deposits: examples from
the Vulsini Volcanoes, Italy. J. Volcanol. Geotherm.
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Peccerillo, A. and Manetti, P. (1985). The potassium
alkaline volcanism of Central-Southern Italy: a
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and flow directions of the Otowi ash flows (lower
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98, 66-76.
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orientation in a concentrated dispersion of elongated
and flattened grains. J. Geol., 76, 457-465.
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Vulsini Volcanic District (Central Italy). Plinius, 4,
91-92.
Santini, L. (1995). Orvieto: Art, History, Folklore. Ed.
Plurigraf S.P.A., Narni (Terni), pp. 95.
Seaman, S.J., McIntosh, W.C., Geissman, J.W.,
Williams, M.L. and Elston, W.E. (1991). Magnetic
fabrics of the Bloodgood Canyon and Shelley Peak
tuffs, southwestern New Mexico: implications for
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dei musei, gallerie, scavi e monumenti d’Italia.
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Vulsini sud-occidentali (caldera di Latera), Boll. Soc.
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Caldera di Latera. Boll. Serv. Geol. It. 90, 61-68.
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Vulsini orientali nell’ambito della Vulcanotettonica
del Complesso. Mem. Soc. Geol. It., 35, 679-687.
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di origine idromagmatica. Boll. G.N.V., 357-372.
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